Curable compositions comprising epoxy resins and styrene have generally been epoxy-polyester compositions wherein a portion of the polyester is replaced with styrene or other ethylenically unsaturated monomer. See, for example, U.S. Pat. Nos. 2,691,007, 3,574,157, and 3,634,542.
Polyether resin and styrene blends are also know. These blends generally exhibit poor processability, short pot life, high viscosity and cure with conventional curing agents to produce products which do not exhibit good physical properties; such as high heat deflection temperatures and retention of physical properties at elevated temperatures. See, for example, U.S. Pat. No. 2,939,859 directed to a polyepoxide/styrene blend cured with peroxides and/or amines. While the compositions of U.S. Pat. No. 2,939,859 do exhibit a reduction of viscosity over an epoxy composition alone, the resulting products do not exhibit high heat deflection temperatures.
Other patents covering polyepoxide/styrene compositions include U.S. Pat. Nos. 3,099,638 and 3,009,898, which are directed to the use of anhydride curing agents, optionally in the presence of a peroxide and/or tertiary amine accelerator.
Another improved composition is that disclosed in U.S. Pat. No. 4,284,753, which claims heat curable epoxy/styrene blends with a carboxyl-containing compound, curing accelerator and free-radical curing agent. However, such compositions lack sufficient flame retardancy for certain applications.
It has now been found that epoxy/styrene blends can be cured with a special curing agent/curing accelerator blend, e.g., an acid anhydride/brominated anhydride in combination with an onium salt, to yield products which exhibit unpredictibly improved physical properties, especially increased heat deflection temperatures and excellent retention of physical properties at elevated temperatures, along with fire retardancy.